This chapter describes the general characteristics of major types of steel annealing, including the process of normalization, which is a process that refines or normalizes the microstructure of steel. The first part of the chapter begins with an overview of the three-stage process of recovery, recrystallization, and grain growth. This is followed by discussions on annealing processes, namely subcritical annealing, critical-range annealing, full annealing, isothermal annealing, annealing for microstructure, and solution or quench annealing. Next, the chapter describes two undesirable reactions that occur during annealing: decarburization and scaling. Information on the gases and gas mixtures used for controlled atmospheres is then provided. The second part of the chapter focuses on the processes involved in normalizing, along with information on furnace equipment for normalizing. In addition, the chapter includes information on processes involved in induction heating of steel.

Heat treatment of steel involves a number of processes to condition the microstructure and obtain desired properties. This includes various methods namely, annealing, normalizing, and hardening by quenching and tempering. This chapter focuses on general heat treatment procedures and the applications of particular types or grades of carbon and low-alloy steels. The discussion covers carbon steel classification for heat treating, tempering of quenched carbon steels, and austempering of steel. In addition, the chapter discusses the effects of alloying and hardenability on steel and provides information on martempering of steel.

The possible classification for tool steels is their division into four groups according to their final application: hot-worked, cold-worked, plastic mold, and high-speed tool steels. This chapter mainly follows such division by application, but the grade nomenclatures used here are primarily from AISI. It presents the classification of tool steels and discusses the principles and processes of tool steel heat treating, namely normalizing, annealing, hardening, and tempering. Various factors associated with distortion in several tool steels are also covered. The chapter discusses the composition, classification, and properties of unalloyed and low-alloy cold-worked tool steels; medium and high-alloy cold-worked tool steels; and 18% nickel maraging steels.

Cast irons, like steels, are iron-carbon alloys but with higher carbon levels than steels to take advantage of eutectic solidification in the binary iron-carbon system. Like steel, heat treatment of cast iron includes stress relieving, annealing, normalizing, through hardening, and surface hardening. This chapter introduces solid-state heat treatment of iron castings, covering general considerations for heat treatment and discussing the processes, advantages, and disadvantages of heat treatment of cast iron.

This chapter provides a practical understanding of heat treatments and how to employ them to optimize the properties and structures of cast irons and steels. It discusses annealing, normalizing, quenching, tempering, patenting, carburizing, nitriding, carbonitriding, and nitrocarburizing. It describes the primary objectives of each treatment along with processing sequences, process parameters, and related phase transformations. The chapter contains more than 100 images, including time-temperature diagrams, transformation curves, data plots, and detailed micro- and macrographs. It also discusses the concepts of hardenability, critical diameter, quench severity, and Jominy testing.

This chapter describes heat treatments that produce uniform grain structures, reduce residual stresses, and improve ductility and machinability. It also discusses spheroidizing treatments that improve strength and toughness by promoting dispersions of spherical carbides in a ferrite matrix. The chapter concludes with a brief discussion on the mechanical properties of ferrite/pearlite microstructures in medium-carbon steels.

This chapter discusses the types, methods, and advantages of heat treating procedures, including annealing, normalizing, tempering, and case hardening. It describes the iron-carbon system, the formation of equilibrium and metastable phases, and the effect of alloy elements on hardenability and tempering response. It discusses the significance of critical temperatures, the use of transformation diagrams, and types of annealing treatments. It also provides information on heat treating furnaces, the effect of heating rate on transformation temperatures, quench and temper procedures, and the use of cold treating.

One of the primary advantages of steels is their ability to attain high strengths through heat treatment while still retaining some degree of ductility. Heat treatments can be used to not only harden steels but also to provide other useful combinations of properties, such as ductility, formability, and machinability. This chapter discusses various heat treatment processes, namely annealing, stress relieving, normalizing, spheroidizing, and hardening by austenitizing, quenching and tempering. It also discusses two types of interrupted quenching processes: martempering and austempering. The chapter concludes with a brief section on temper embrittlement.

This chapter introduces the principal heat treating processes, namely normalizing, annealing, stress relieving, surface hardening, quenching, and tempering. An overview of four of the more popular surface hardening treatments, namely carburizing, carbonitriding, nitriding, and nitrocarburizing, is provided.

This chapter is a detailed account of heat treating techniques for cast irons (gray and ductile), providing the reader with a basic understanding of the differences among various types of cast irons and the concept of carbon equivalent. The types of heat treatments discussed are stress relieving, annealing, normalizing, surface hardening, quenching, martempering, austempering, and flame and induction hardening.

The through-hardening process is generally used for gears that do not require high surface hardness. Four different methods of heat treatment are primarily used for through-hardened gears. In ascending order of achievable hardness, these methods are annealing, normalizing and annealing, normalizing and tempering, and quenching and tempering. This chapter discusses the processes involved in the through-hardening of gears. It provides information on designing procedures, hardness, distortion, and applications of the through-hardened gears. The chapter presents a case history on the design and manufacture of a through-hardened gear rack.

This article covers the metallurgy and properties of gray irons. It describes the classes or grades of gray iron, the types of applications for which they are suited, and the corresponding compositional ranges. It discusses the role of major, minor, and trace elements, how they are added, and how they affect various properties, behaviors, and processing characteristics. It explains how silicon, chromium, and nickel, in particular, improve high-temperature, corrosion, and wear performance.

This article discusses the metallurgy and properties of ductile cast iron. It begins with an overview of ductile or spheroidal-graphite iron, describing the specifications, applications, and compositions. It then discusses the importance of composition control and explains how various alloying elements affect the properties, behaviors, and processing characteristics of ductile iron. The article describes the benefits of nickel and silicon additions in particular detail, explaining how they make ductile iron more resistant to corrosion, heat, and wear.

Modern gears are made from a wide variety of materials. Of all these, steel has the outstanding characteristics of high strength per unit volume and low cost per pound. Although both plain carbon and alloy steels with equal hardness exhibit equal tensile strengths, alloy steels are preferred because of higher hardenability and the desired microstructures of the hardened case and core needed for the high fatigue strength of gears. This chapter provides an overview of the key considerations involved in the selection and application of heat treating processes for alloy steel gears and serves as an introduction to the subsequent chapters in this book.

The properties of steel are affected markedly as the percentage of carbon varies. This chapter describes the properties of alloys of iron and carbon, including a review of the iron-carbon phase diagram and, in particular, the portion of the diagram relevant to carbon steels. It addresses the processes involved in the transformation (decomposition) of austenite to achieve various microstructures.

This chapter introduces the fundamental considerations involved in heat treating of gears and the primary processes used, namely, through-hardening, carburizing and hardening, nitriding, carbonitriding, and induction hardening.

Through-hardening heat treatment is generally used for gears that do not require high surface hardness. In through hardening, gears are first heated to a required temperature and then cooled either in the furnace or quenched in air, gas, or liquid. Four heat treatment methods are primarily used for through-hardened gears: annealing, normalizing and annealing, normalizing and tempering, and quenching and tempering. This chapter begins with a discussion of these through-hardening processes. This is followed by sections providing some factors affecting the design and hardness levels of through-hardened gears. Next, the chapter reviews the considerations related to distortion of through-hardened gears. It then discusses the applications of through-hardened gears. Finally, the chapter presents a case history of the design and manufacture of a through-hardened gear rack.

The primary objective of carburizing and hardening gears is to secure a hard case and a relatively soft but tough core. For this process, low-carbon steels (up to a maximum of approximately 0.30% carbon), either with or without alloying elements (nickel, chromium, manganese, molybdenum), normally are used. The processes involved in hardening, tempering, recarburizing, and cold treatment of carburized and quenched gears are discussed. Next, the chapter reviews the selection of materials for carburized gears and considerations related to carbon content, core hardness, and microstructure. This is followed by sections discussing some problems that can be experienced in the carburizing process and how these can be addressed, including a section on shot peening to induce compressive residual stress at and below the surface. It then discusses the applications of carburized gears and finally presents a case history of distortion control of carburized and hardened gears.

Nitriding is a case-hardening process used for alloy steel gears and is quite similar to case carburizing. Nitriding of gears can be done in either a gas or liquid medium containing nitrogen. This chapter discusses the processes involved in gas nitriding. It reviews the effects of white layer formation in nitrided gears and presents general recommendations for nitrided gears. The chapter describes the microstructure, overload and fatigue damage, bending-fatigue life, cost, and distortion of nitrided gears. Information on nitriding steels used in Europe and the applications of nitrided gears are also provided. The chapter presents case studies on successful nitriding of a gear and on the failure of nitrided gears used in a gearbox subjected to a load with wide fluctuations.

Several limitations in achieving optimal gear performance with conventional nitriding have led researchers to work on a variety of novel and improved nitriding processes. Of these, ion/plasma nitriding offers some promising results, which are reviewed in this chapter. The chapter concludes with a case history describing the application of ion nitriding to an internal ring gear of an epicyclic gearbox.